How to copy all drawable images into SD Card

How to copy all drawable images into SD Card

I want to copy all drawable images into SD Card in a specific folder which
i have created using this code in onCreate() method :
File wallpaperDirectory = new File("/sdcard/Wallpaper");
wallpaperDirectory.mkdirs();
I have 6 images in my drawable folder and i want to copy all those images
into Wallpaper folder....
I have given below permission to work with SD Card
<uses-permission
android:name="android.permission.WRITE_EXTERNAL_STORAGE"
></uses-permission>